1. Field of the Invention
This invention relates to a dielectric capacitor manufacturing method and a semiconductor storage device manufacturing method especially suitable for use in fabrication of a dielectric capacitor using a dielectric film made of a dielectric material with a perovskite type crystal structure and fabrication of a semiconductor storage device having such a dielectric capacitor.
2. Description of the Related Art
Recently, the area of a memory cell was rapidly reduced along with an increase in storage capacitance of semiconductor storage devices. Concurrently, in a capacitor forming a memory cell, efforts are made to ensure a required charge capacitance by employing a three-dimensional complex structure. Under these circumstances, in the attempt of improving the production yield and reducing the steps of the manufacturing process by simplification of the construction, researches are made toward employment of a dielectric capacitor simplified in construction by using a dielectric film with a high dielectric constant. Known as a dielectric film with a high capacitor is one having a perovskite type crystalline structure and made of a polycrystalline oxide with a grain size of 20 to 300 nm, approximately.
A conventional technique for making a dielectric capacitor using a dielectric film made of a dielectric material with a perovskite type crystalline structure was configured to first make a dielectric film on a lower electrode in form of a film on a substrate, then anneal the dielectric film to crystallize it, further make an upper electrode on the crystallized dielectric film, and pattern the upper electrode, dielectric film and lower electrode into the form of a dielectric capacitor by etching, using reactive ion etching (RIE) or ion milling.
However, in the case where a dielectric capacitor using a dielectric film made of a dielectric material with a perovskite type crystalline structure was made by the conventional technique, there was the problem that the characteristics of the dielectric capacitor after treatment deteriorated significantly due to etching of a certain element or shortage of oxygen along the treated surface of the dielectric film during etching by RIE or ion milling. Especially when the area of the dielectric capacitor was reduced below 10 xcexcm2, particularly, several xcexcm2, along with large-scaling of semiconductor memory, there was a tendency toward an increase of the area occupied by individual crystal grains in the dielectric film relative to the entire area of the capacitor, hence a relative increase of influences from damages of individual crystal grains belonging to side wall portions of the capacitor during etching process, an increase of deterioration of characteristics of the dielectric capacitor.
Moreover, in the case where a dielectric capacitor using a dielectric film made of a dielectric material with a perovskite type crystalline structure was made by the conventional technique, there was a tendency toward an increase of the leak current of the dielectric capacitor due to deposition of a certain metal or generation of a conductive oxide on side walls of the dielectric capacitor during the etching process or the subsequent annealing process especially in large-capacity semiconductor memory in which the area of the dielectric capacitor is reduced below 10 xcexcm2, particularly, several xcexcm2, and it was a serious reason adversely affecting the reliability.
It is therefore an object of the invention to provide a dielectric capacitor manufacturing method and a semiconductor storage device manufacturing method capable of realizing a dielectric capacitor exhibiting good characteristics even when the area of dielectric capacitor is reduced upon manufacturing the dielectric capacitor using a dielectric film with a perovskite type crystalline structure and a semiconductor storage device including the dielectric capacitor.
Another object of the invention is to provide a dielectric capacitor manufacturing method and a semiconductor storage device manufacturing method capable of realizing a dielectric capacitor having exhibiting good characteristics and improving the reliability even when the area of the dielectric capacitor is reduced upon manufacturing the dielectric capacitor using a dielectric film with a perovskite type crystalline structure and a semiconductor storage device including the dielectric capacitor.
According to the first aspect of the invention, there is provided a method for manufacturing a dielectric capacitor using a dielectric film made of a dielectric material with a perovskite type crystalline structure, comprising the steps of:
making a lower electrode;
making on the lower electrode a precursor film having as its major component an amorphous phase or a fluorite phase of components elements of the dielectric material;
making an upper electrode on the precursor patterning at least the upper electrode and the precursor film into the form of the dielectric capacitor by etching; and
annealing the precursor film patterned into the form of the dielectric capacitor to change the amorphous phase or the fluorite phase to a crystal phase of a perovskite type crystalline structure and obtain the dielectric film.
According to the second aspect of the invention, there is provided a method for manufacturing a dielectric capacitor using a dielectric film made of a dielectric material with a perovskite type crystalline structure, comprising the steps of:
making a lower electrode;
making on the lower electrode a precursor film having as its major component an amorphous phase or a fluorite phase of components elements of the dielectric material;
making an upper electrode on the precursor film;
patterning the upper electrode and the precursor film into the form of the dielectric capacitor by etching;
making a protective coat which covers side walls of the upper electrode and the precursor film patterned into the form of the dielectric capacitor; and
annealing the precursor film patterned into the form of the dielectric capacitor and having the protective coat on the side walls to change the amorphous phase or the fluorite phase to a crystal phase of a perovskite type crystalline structure and obtain the dielectric film.
According to the third aspect of the invention, there is provided a method for manufacturing a semiconductor storage device having a dielectric capacitor using a dielectric film made of a dielectric material with a perovskite type crystalline structure, comprising the steps of:
making a lower electrode of the dielectric capacitor;
making on the lower electrode a precursor film having as its major component an amorphous phase or a fluorite phase of components elements of the dielectric material;
making an upper electrode on the precursor film;
patterning at least the upper electrode and the precursor film into the form of the dielectric capacitor by etching; and
annealing the precursor film patterned into the form of the dielectric capacitor to change the amorphous phase or the fluorite phase to a crystal phase of a perovskite type crystalline structure and obtain the dielectric film.
According to the fourth aspect of the invention, there is provided a method for manufacturing a semiconductor storage device having a dielectric capacitor using a dielectric film made of a dielectric material with a perovskite type crystalline structure, comprising the steps of:
making a lower electrode of the dielectric capacitor;
making on the lower electrode a precursor film having as its major component an amorphous phase or a fluorite phase of components elements of the dielectric material;
making an upper electrode on the precursor film;
patterning the upper electrode and the precursor film into the form of the dielectric capacitor by etching;
making a protective coat which covers side walls of the upper electrode and the precursor film patterned into the form of the dielectric capacitor; and
annealing the precursor film patterned into the form of the dielectric capacitor and having the protective coat on the side walls to change the amorphous phase or the fluorite phase to a crystal phase of a perovskite type crystalline structure and obtain the dielectric film.
In the present invention, typically used as the precursor film is a film having as its major component an amorphous phase or a fluorite phase of Bi, Sr, Ta, Nb and O (its atomic composition ratio being in the range of 2.0xe2x89xa62Bi/(Ta+Nb)xe2x89xa62.6 and 0.6xe2x89xa62Sr/(Ta+Nb)xe2x89xa61.2). In this case, by annealing the precursor film, there is obtained a dielectric film (SBT film) of a ferroelectric material with a Bi layered structured perovskite type crystalline structure having the composition formula BixSry(TazNb1-z)2.0Ow (where 2.0xe2x89xa6xxe2x89xa62.6, 0.6xe2x89xa6yxe2x89xa61.2, 0xe2x89xa6zxe2x89xa61.0, w=9xc2x1d, 0xe2x89xa6dxe2x89xa61.0). Alternatively, the precursor film of SBT may be made by first making on the lower electrode a film having as its major component an amorphous phase of Bi, Sr, Ta, Nb and O (its atomic composition ratio being in the range of 2.0xe2x89xa62Bi/(Ta+Nb)xe2x89xa62.6 and 0.6xe2x89xa62Sr/(Ta+Nb)xe2x89xa61.2), and then annealing it to change the amorphous phase to a fluorite phase. In this case, annealing is preferably conducted prior to making the upper electrode.
In the present invention, also usable as the precursor film is a film having as its major component an amorphous phase or a fluorite phase of Bi, Sr, Ta, Nb, Ti and O (its atomic composition ratio being in the range of 0.6xe2x89xa62Sr/(Ta+Nb)xe2x89xa61.2, 1.7xe2x89xa62Bi/(Ta+Nb)xe2x89xa62.5, and 0 less than 2Ti/(Ta+Nb)xe2x89xa61.0). The atomic composition ratio of the precursor film having as its major component the amorphous phase of the fluorite phase of Bi, Sr, Ta, Nb, Ti and O is preferably in the range of 0.7xe2x89xa62Sr/(Ta+Nb)xe2x89xa61.0, 2.0xe2x89xa62Bi/(Ta+Nb)xe2x89xa62.4, and 0.01xe2x89xa62Ti/(Ta+Nb)xe2x89xa61.0)
As to 2Ti/(Ta+Nb), it more preferably satisfies 0.1xe2x89xa62Ti/(Ta+Nb)xe2x89xa61.0. In this case, by annealing the precursor film, there is obtained a dielectric film (SBTT film) of a ferroelectric material with a Bi layered structured perovskite type crystalline structure having the composition formula SrxBiy(Ta, Nb)2.0TizOw (where 0.6xe2x89xa6xxe2x89xa61.2, 1.7xe2x89xa6yxe2x89xa62.5, 0 less than zxe2x89xa61.0, w=9÷d, 0xe2x89xa6dxe2x89xa61.0, preferably 0.7xe2x89xa6xxe2x89xa61.0, 2.0xe2x89xa6yxe2x89xa62.4, 0.01xe2x89xa6zxe2x89xa61.0, w=9xc2x1d, 0xe2x89xa6dxe2x89xa61.0, more preferably 0.7xe2x89xa6xxe2x89xa61.0, 2.0xe2x89xa6yxe2x89xa62.4, 0.1xe2x89xa6zxe2x89xa61.0, w=9xc2x1d, 0xe2x89xa6dxe2x89xa61.0). Alternatively, the precursor film of SBTT may be made by first making on the lower electrode a film having as its major component an amorphous phase of Bi, Sr, Ta, Nb, Ti and O (in which the atomic composition ratio on the lower electrode (its atomic composition ratio being in the range of 0.6xe2x89xa62Sr/(Ta+Nb)xe2x89xa61.2, 1.7xe2x89xa62Bi/(Ta+Nb)xe2x89xa62.5, and 0xe2x89xa62Ti/(Ta+Nb)xe2x89xa61.0), and then annealing it to change the amorphous phase to a fluorite phase. In this case, annealing is preferably conducted prior to making the upper electrode.
In the present invention, also usable as the precursor film is a film having as its major component an amorphous phase of Pb, Zr, Ti and O (its atomic composition ratio being in the range of 0.1xe2x89xa6Zr/Pbxe2x89xa60.6 and 0.4xe2x89xa6Ti/Pbxe2x89xa60.9) or a film containing as its major component an amorphous phase of Pb, Zr, Ti, Nb and O (its atomic composition ratio being in the range of 0.1xe2x89xa6Zr/Pbxe2x89xa60.6, 0.4xe2x89xa6Ti/Pbxe2x89xa60.9 and 0.03xe2x89xa6Nb/Pbxe2x89xa60.30). In the former case, by annealing the precursor film, there is obtained a dielectric film (PZT) film of a ferroelectric material having a perovskite type crystalline structure expressed by the composition formula Pb1.0(ZrxTi1-x)1.0O3 (where 0.1xe2x89xa6xxe2x89xa60.6). In the latter case, by annealing the precursor film, there is obtained a dielectric film (PNZT film) of a ferroelectric film having a perovskite type crystalline structure expressed by the composition formula Pb1.0-yNby(ZrxTi1-x)1.0O3 (where 0.1xe2x89xa6xxe2x89xa60.6, 0.03xe2x89xa6yxe2x89xa60.30).
Ferroelectric materials indicated above are suitable for use as the material of a ferroelectric film of ferroelectric memory.
In the present invention, also usable as the precursor film is a film having as its major component an amorphous phase of Ba, Sr, Ti and O (its atomic composition ratio being in the range of 0xe2x89xa6Sr/Tixe2x89xa61.0 and 0xe2x89xa6Ba/Tixe2x89xa61.0) . In this case, by annealing the precursor film, there is obtained a dielectric film (BST film) of a high-dielectric material expressed by the composition formula (BaxSr1-x)1.0Ti1.0O3 (where 0xe2x89xa6xxe2x89xa61.0). The high-dielectric material is suitable for use as the material of a dielectric film of a capacitor in DRAM, for example.
In the present invention, the precursor film is made by, for example, chemical vapor deposition, such as metal organic chemical vapor deposition, or spin-coating.
In the present invention, if the finally obtained dielectric film is a SBTT film, the precursor film is preferably made by forming a film having as its major component a fluorite phase by metal organic chemical vapor deposition or other chemical vapor deposition. In this case, the film having the fluorite phase as its major component is made under a growth temperature (substrate temperature) between 400xc2x0 C. and 650xc2x0 C., for example, under a reaction gas pressure of 1 to 10 Torr, for example. Used as the reaction gas is a mixed gas made by mixing an oxidizable gas with a mixed gas containing predetermined composition ratios of, for example, at least one organic metal source material selected from a first group consisting of Bi(C6H5)3, Bi(o-C7H7)3, Bi(O-C2H5)3, Bi(O-iC3H7)3, Bi(O-tC4H9)3 and Bi(O-tC5H11)3, at least one organic metal source material selected from a second group consisting of Sr(THD)2, Sr(THD)2 tetraglyme (THD:2,2,6,6-tetramethyl-3,5-heptandion,C11H19O2) and Sr(Me5C5)2xc2x72THF(Me:CH3, THF: tetrahydrofuran, at least one organic metal source material selected from a third group consisting of Ti(i-OC3H7)4, TiO(THD)2 and Ti(THD)2(i-OC3H7)2, and at least one organic metal source material selected from a fourth group consisting of Ta(i-OC3H7)5, Ta(i-OC3H7)4THD, Nb(i-OC3H7)5 and Nb(i-OC3H7)4THD.
When the finally obtained dielectric film is a SBTT film, the precursor film may be made by first making a film having an amorphous phase as its major component on the lower electrode and then changing the amorphous phase into a fluorite phase by annealing. More specifically, the precursor film is preferably made by first forming the film having the amorphous phase as its major component by metal organic or other chemical vapor deposition and then annealing it in an oxidizable gas atmosphere. In this case, the film having the amorphous phase as its major component is made at a temperature (substrate temperature) between 300xc2x0 C. and 500xc2x0 C., for example, and a reaction gas pressure of 1 to 10 Torr, for example. The annealing made here is conducted at a temperature between 600xc2x0 C. and 850xc2x0 C., for example, for 30 seconds to 120 minutes, for example. Used here as the reaction gas is: a mixed gas made by mixing an oxidizable gas with a mixed gas containing predetermined composition ratios of, for example, at least one organic metal source material selected from a first group consisting of Bi(C6H5)3, Bi(o-C7H7)3, Bi(O-C2H5)3, Bi(o-iC3H7)3, Bi(O-tC4H9)3 and Bi(O-tC5H11)3, at least one organic metal source material selected from a second group consisting of Sr(THD)2, Sr(THD)2 tetraglyme and Sr(Me5C5)2xc2x72THF, at least one organic metal source material selected from a third group consisting of Ti(i-OC3H7)4, TiO(THD)2 and Ti(THD)2(i-OC3H7)2, and at least one organic metal source material selected from a fourth group consisting of Ta(i-OC3H7)5, Ta(i-OC3H7)4THD, Nb(i-OC3H7)5 and Nb(i-OC3H7)4THD; or a mixed gas made by mixing predetermined composition ratios of, for example, at least one organic metal source material selected from a first group consisting of Bi(C6H5)3, Bi(o-C7H7)3, Bi(O-C2H5)3, Bi(O-iC3H7)3, Bi(O-tC4H9)3 and Bi(O-tC5H11)3, at least one organic metal source material selected from a second group consisting of SrTa2(OC2H5)12 and SrNb2(OC2H5)12 (bimetallic alcoxide), and at least one organic metal source material selected from a third group consisting of Ti(i-OC3H7)4, TiO(THD)2 and Ti(THD)2(i-OC3H7)2.
In the present invention, for obtaining a dielectric film, the precursor film patterned into the form of a dielectric capacitor is typically annealed in an oxidizable gas atmosphere, and the annealing in the oxidizable gas atmosphere is conducted at a temperature preferably between 500xc2x0 C. and 900xc2x0 C., or more preferably between 650xc2x0 C. and 800xc2x0 C. Alternatively, for obtaining the dielectric film, the precursor film patterned into the form of the dielectric capacitor may be first annealed in a nitrogen gas atmosphere at a temperature between 500xc2x0 C. and 900xc2x0 C. and then annealed in an oxidizable gas atmosphere at a temperature between 500xc2x0 C. and 900xc2x0 C.; or may be first annealed in a nitrogen gas atmosphere at a temperature between 500xc2x0 C. and 900xc2x0 C. and then annealed in an oxidizable gas atmosphere containing 0.5% or more of ozone at a temperature between 300xc2x0 C. and 600xc2x0 C.; or may be first annealed in a reduced pressure atmosphere of 100 Torr or less at a temperature between 500xc2x0 C. and 800xc2x0 C. and then annealed in an oxidizable gas atmosphere containing 0.5% or more of ozone at a temperature between 300xc2x0 C. and 600xc2x0 C.
In the present invention, the thickness of the dielectric film is selected between, for example, 20 nm and 200 nm. From the viewpoint of realizing better characteristics, the thickness of the dielectric film is preferably selected between 20 nm and 100 nm. From the viewpoint of realizing low-voltage performance of a semiconductor device using the dielectric capacitor, the thickness of the dielectric film is more preferably selected between 30 nm and 80 nm.
In the first and third aspects of the invention, the step of patterning at least the upper electrode and the precursor film into the form of the dielectric capacitor by etching is typically performed by reactive ion etching or ion milling, for example. Similarly, in the second and fourth aspects of the invention, the step of patterning the upper electrode and the precursor film into the form of the dielectric capacitor by etching is typically performed by reactive ion etching or ion milling.
In the second and fourth aspects of the invention, the protective coat is typically an insulating film. combination of the material of the protective coat and the material of the dielectric film, i.e., combination of the material of the protective coat and the material of the precursor film, is preferably chosen so that any component element in one off the materials does not react on any component element of the other material or, if they reacts, they make a stable insulating film. From this viewpoint, used as the material of the protective coat is, for example, SrTa2O6, Ta2O5, Nb2O5, ZrO2, CeO2, Y2O3 or HfO2 depending upon component elements of the dielectric film.
According to the first or third aspect of the invention having the above-explained construction, when a dielectric capacitor using as a dielectric film a dielectric material with a perovskite type crystalline structure is made, a lower electrode, a precursor film having as its major component an amorphous phase of fluorite phase of component elements of the dielectric material and an upper electrode are formed sequentially, and at least the upper electrode and the precursor film are patterned into the form of the dielectric capacitor by etching. Thereafter, the precursor film patterned into the form of the dielectric capacitor is annealed to change the amorphous phase or the fluorite phase into a crystal phase with the perovskite type crystalline structure and to thereby obtain the dielectric film. Therefore, crystal grains in the finally obtained dielectric film are not damaged by etching, and the dielectric capacitor can be prevented from deterioration in characteristics by etching.
According to the second or fourth aspect of the invention having the above-explained construction, when fabricating a dielectric capacitor using a dielectric material with a perovskite type crystalline structure as its dielectric film, a lower electrode, a precursor film having an amorphous phase of fluorite phase of component elements of the dielectric material as its major component and an upper electrode are formed sequentially, and the upper electrode and the precursor film are patterned into the form of the dielectric capacitor by etching. Thereafter, a protective coat is made to cover side walls of the upper electrode and the precursor film. Therefore, it is prevented that a certain metal deposits on side walls of the dielectric capacitor or a conductive oxide is generated upon etching of the lower electrode or subsequent annealing, and the dielectric capacitor is therefore prevented from deterioration in leak current characteristics. Additionally, according to the second and fourth aspects of the invention, since the dielectric film is obtained by annealing the precursor film patterned into the form of the dielectric capacitor like the first and third aspects of the invention, the dielectric capacitor is prevented from deterioration in characteristics by etching.